It's been a year since I switched all my personal projects from Bitbucket / Mercurial to Github / Git, so I think the time is right for a brief recap.
As I mentioned back then, the platform (Github vs. Bitbucket) served a larger role in the decision to switch than the source control system (Git vs. Mercurial). Bitbucket lets you use Git now if you want, so the latter difference is actually moot. It's the platform that remains the difference, and if I felt that Github has "won" the platform war a year ago, I feel even more so now. Even so far as being called the new résumé for developers, Github has definitely captured a very prominent place in the jargon and habits of our craft.
Amazingly, Bitbucket still hasn't caught up in terms of front-page information. On Github it's fairly easy, in a quick glance, to assess how active a developer is, which projects he contributes to, etc. On Bitbucket, all you see is a dull list of project names, not sorted in any useful way. Organizations, another cool Github concept, is also nowhere to be seen. Perhaps Bitbucket gave up on this fight, though, focusing on corporate users.
My main qualm with Bitbucket was that due to its lack of popularity I didn't get as much contribution to my projects as I hoped for. Had this improved? Certainly! Instead of "why don't you use Github" complaints, I now routinely get pull requests (or at least opened issues) for my projects. Several of my projects are starred by dozens of developers, and the most popular one - pycparser - now has over 40 forks!
Github pull requests are indeed a thing of beauty. Not that there's anything technically complex about them. It's a cultural thing. If you find a problem in a project, just send in a pull request. Most chances are it will be accepted. Pull requests have become a ubiquitous contribution currency, because of one very subtle, yet powerful factor. Github pull requests are part of your online identity. Once your pull request is merged into a project, it's forever retained in the log that you have contributed to that project. You being the direct link to your Github account / profile. For example, I commited a small fix to Django a few months ago - here it is, forever recorded and linked to my Github profile. The power of Github as the de-facto social network of developers cannot be ignored. It is way, way more significant than Linkedin.
Let's put it this way - actual commits beat empty endorsements, any day.
Github indeed serves the résumé role well, at least for me. I routinely receive job / interview offers or recruiter pitches based on my "impressive Github profile".
Even projects that are not formally hosted on Github take care to maintain a mirror there, because Github is such a familiar low-entry way to examine their code and even fork it. It's not uncommon for people to develop their changes in branches vs. the Github mirror, and sending patches to the real source repository when done. I know this happens in the LLVM & Clang world a lot. Maintaining Github mirrors of projects is quite easy - for example, it took me just a few hours to set up this semi-official Github mirror for CPython, and as for maintaining it... well, there's cron for that.
Github's popularity is also the cause of it being the first target of other projects that aim to make the life of developers easier. Travis CI is a blessing, and I use its Github integration extensively. All developers know how painful it is to set up and maintain continuous integration builds for their project. Travis & Github make this ridiculously easy, at least for the limited set of platforms Travis currently supports. Automatically run tests for each proposed pull request and tell me if it breaks anything? Shut up and take my money! Oh, it's free for open-source projects...